The present invention relates to an apparatus for manufacturing large-surface, band-shaped silicon for solar cells. The manufacturing process of silicon for solar cells includes the continuous layering of a net-like structured graphite carrier, which, although resistant to silicon smelt, can be wetted by the smelt. The arrangement furthermore includes:
(a) a melting pot for receiving the silicon smelt, whereby the floor of the melting pot has been provided with a vertical, and out-ward extending drain opening for forwarding the smelt to the carrier unit; and
(b) a horizontally arranged, heatable canal located below the melting pot in the area of the drain opening to guide the carrier unit.
It is recommended that reasonably priced silicon be used for the manufacture of solar cells. The requirements with respect to crystal quality are not as stringent as those for semi-conductor components applied in conjunction with integrated circuits. Therefore, efforts were made to find the means to manufacture silicon crystals in the simplest and most cost effective manner, that is to say, without material waste.
A method for manufacturing cheap silicon is known through German patent document DE-OS No. 28 50 805. With this method silicon sheets for solar cells can be produced at a high output rate (approx. 1 m.sup.2 /min.) by moving a carrier unit, consisting of graphite and provided with holes, during an extraction procedure in a slightly curved mode across the surface of the silicon smelt, whereby the carrier unit is integrated in the silicon body formed by the crystalization of the silicon.
In this case the convection currents present in the smelt pose technical difficulties, since these currents lead to considerable temperature fluctuations at the crystalization front and consequently affect the thickness of the plane-shaped silicon body. It is also difficult to feed the silicon smelt continuously and consistently to maintain an unchanging smelting level, which is considered a necessary prerequisite for the uniform layering of the carrier unit.
An additional improvement with respect to the crystal quality and the uniformity of the layering process is achieved by the kind of configuration mentioned in the introduction, which has been already proposed in the German patent application No. 32 31 326.8. As can be seen in FIG. 1 of this application, a net-like carrier unit is inserted in a horizontally arranged canal extending below a melting pot provided with drain openings. Subsequently the net-like carrier unit is brought into contact with the silicon smelt to be followed by the crystalization of the silicon in the loops of the net. In accordance with this layering configuration, the maximum loop size to be filled is limited to 5.times.5 mm.sup.2 and does not guarantee uniform layering procedures, because this configuration does not provide the proper control to regulate the flow of silicon into the layering canal or in the melting pot. It has been established, that the silicon smelt present in the canal might spill over as soon the smelt has exceeded a certain critical volume.